Mono-tertiary butylhydroquinone (MTBHQ) is a compound which has been shown to possess excellent antioxidant properties with a concomitant low toxicity. The compound is utilized as an antioxidant in the food industry or as an intermediate in the preparation of other chemicals. MTBHQ is used as an antioxidant for fat, lards, oils and fat-containing food, either by incorporation into the food stuff itself or by being incorporated in the material which is used to encase or wrap the particular food stuff. In addition, the use of this compound is likely to increase in the future due to the low toxicity and higher solubility which the process relates to butylated hydroxyanisole (BHA) which heretofor has been widely used as an antioxidant in foods.
Other possible uses for this compound could include the use as a stabilizer in irradiated polypropylene, as an inhibitor for unsaturated polyester, as a stabilizer for polyethylene glycol or other polymerizable systems and to improve the color stability of gasoline antioxidants.
One method of preparing this compound is to alkylate hydroquinone with an alkylating agent such as the olefin, isobutylene, or the alcohol, t-butyl alcohol, said reaction being effected in the presence of an acidic catalyst and in a reaction medium comprising a hydrocarbon solvent. However, certain deficiencies are present in this process which renders said process difficult to effect at an acceptable economical return. For example, when utilizing hydrocarbon solvent such as xylene for the reaction medium, an elaborate work-up section is required due to the fact that the presence of xylene in the reaction product requires azeotropic distillation with water followed by a number of crystallization steps to improve the purity of the final product. In addition, an object of the process is to obtain the mono-alkylated product in as great a yeild as possible. Inasmuch as the amount of di-alkylated product which is formed during the reaction is present in an inordinant amount, it is necessary to separate the two compounds in order to provide an effective antioxidant compound. The separation step which may be necessary therefore entails an additional operating procedure as well as requiring additional equipment, all of which adds to the overall cost of the process, thereby reducing the return on the finished product.
As will hereinafter be shown in greater detail, it has now been discovered that by effecting the alkylation reaction in a reaction medium of a certain type, it is possible to obtain a greater amount of mono-alkylated product while concomitantly increasing the selectivity to the desired product.